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In signal processing and related disciplines, aliasing is the overlapping of frequency components resulting from a sample rate below the Nyquist rate.This overlap results in distortion or artifacts when the signal is reconstructed from samples which causes the reconstructed signal to differ from the original continuous signal.
Range aliasing occurs when reflections arrive from distances that exceed the distance between transmit pulses at a specific pulse repetition frequency (PRF). Range ambiguity resolution is required to obtain the true range when the measurements are made using a system where the following inequality is true.
Pulse-Doppler ambiguity zones. Each blue zone with no label represents a velocity/range combination that will be folded into the unambiguous zone. Areas outside the blue zones are blind ranges and blind velocities, which are filled in using multiple PRF and frequency agility. The unambiguous zone is in the lower left corner.
Radial velocity aliasing occurs when reflections arrive from reflectors moving fast enough for the Doppler frequency to exceed the pulse repetition frequency (PRF). Frequency ambiguity resolution is required to obtain the true radial velocity when the measurements is made using a system where the following inequality is true.
The disadvantage of pulsed Doppler is that the measurements can suffer from aliasing. The terms Doppler ultrasound and Doppler sonography have been accepted to apply to both pulsed and continuous Doppler systems, despite the different mechanisms by which the velocity is measured. [citation needed] There are no standards for displaying color ...
Ringing artifacts pose a problem with search, detection, and ambiguity resolution in pulse-Doppler radar. Ringing is reduced in two ways. First, the shape of the transmit pulse is adjusted to smooth the leading edge and trailing edge so that RF power is increased and decreased without an abrupt change.
This image was scaled up using nearest-neighbor interpolation.Thus, the "jaggies" on the edges of the symbols became more prominent. Jaggies are artifacts in raster images, most frequently from aliasing, [1] which in turn is often caused by non-linear mixing effects producing high-frequency components, or missing or poor anti-aliasing filtering prior to sampling.
Spikes may be caused by aliasing of the Doppler signal. McLelland and Nicholas [2] explained the physical processes while Nikora and Goring, [5] Goring and Nikora [10] and Wahl [11] developed techniques to eliminate aliasing errors called "spikes". These methods were developed for steady flow situations and tested in man-made channels.